1. Field of the Invention
The present invention relates generally to devices for modulating an optical signal and more specifically to retroreflecting devices useful for modulating optical signals.
2. Description of the Background Art
Secure optical communications with satellites or other remote platforms requires that the response to an interrogating light beam be directed back precisely to the source of the light beam. Therefore, the incorporation of a modulated retroreflector, which always reflects light back to its source, into a remote platform was proposed as early as the 1940's. Unfortunately, during the 1940's, materials did not exist to sustain a high data at practicable driver power levels. That is, the drive power levels would dictate payloads comparable in bulk and weight to RF payloads. Since then, ferro-electric liquid crystal (FLC) technology has evolved to provide a potentially low power shutter. FLC modulators, however, modulation rates of only a few kilohertz, which severely limits their bandwidth.
Fritz et al., Appl. Phys. Lett. 63(4), Jul. 26, 1993, the entirety of which is incorporated herein by reference, disclose a retroreflecting optical modulator in which the retroreflector is modulated by a Fabry-Perot resonator. Fabry-Perot resonators, however, are highly sensitive to the change in the angle of the source light, as well as changes in temperature.